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White Sands Gypsum Desert

Most sand deserts consist of quartz sand, but White Sands has got its name because its main constituent is (white) gypsum. Normally desert sand becomes extremely hot when the sun is shining, but the white gypsum in White Sands reflect most of the sun radiation back into the atmosphere (albedo effect) so that the desert remains relatively cool.

The White Sands in New Mexico is the world’s largest gypsum dune field, stretching over 710 km2. Gypsum is rarely found in the form of sand because it is water-soluble. Normally, rain would dissolve the gypsum and carry it to the sea. The basin, in which the White sands lie, is enclosed and has no outlet to the sea, so that rain that dissolves gypsum from the surrounding mountains is trapped within the basin. Thus water either sinks into the ground or forms shallow pools which subsequently dry out and leave gypsum in a crystalline form, called selenite, on the surface. During the last ice age, a lake covered much of the basin. When it dried out, it left a large flat area of selenite crystals. Another lake is a dry lake bed, at one of the lowest points of the basin, which occasionally fills with water. Much of the ground is covered with selenite crystals which reach lengths of up to 1 m. Weathering and erosion eventually breaks the crystals into sand-size grains that are carried away by the prevailing winds from the southwest, forming white dunes. Winds occasionally lift the gypsum sands into the air. A gypsum dust storm emerged from the dunes in late February 2012.

The dust blowing out of White Sands National Monument was part of a larger pattern of dust storms in the region, including dust in Mexico, Kansas, and Oklahoma.

In Danish:

Albedo is the fraction of solar energy (shortwave radiation) reflected from the Earth back into space. It is a measure of the reflectivity of the earth's surface. | Impressum